Freshwater flush

Is it feasable to install the flush tube on an older model 2 stroke 150 Yamaha. The boats in the slip and would love to easily flush them out. Currently using the muffs underwater, works but only so so. Any ideas?. Thanks.

GW 232GT Gulfstream
150Yam x 2
“3rd Day”
Gen. Chap.1 Vs.9-13